The GAD genes, regulated in part by EvgS, have also been implicated in some aspects of pathogenicity of E. coli in a number of studies (e.g., Tree et al., 2011; Branchu et al., 2014), so understanding the novel effects of indole reported in this paper may enhance our understanding of the complex interactions between E. coli and the gut environment that lead to colonization and, in some cases, infection. Here, GAD1 is linked to infection.